Werner chromium complexes and methods for their preparation

ABSTRACT

A WERNER COMPLEX COMPOSITION HAS TRIVALENT CHROMIUM ATOMS COORDINATED WITH ACIDO GROUPS AND CHLORINE ATOMS. THE ACIDO GROUPS ARE FROM SATURATED ALIPHATIC DICARBOXYLIC ACIDS HAVING LESS THAN SIX CARBON ATOMS AND THAT MAY CONTAIN HYDROXYL GROUPS, BUT NOT MORE THAN THREE HYDROXYL GROUPS. THE COMPLEEXES ARE CHARACTERIZED BY A SPECIFIC RANGE FOR THE RATIO OF BOTH THE CHROMIUM ATOMS TO ACIDO GROUPS AS WELL AS CHROMIUM ATOMS TO CHLORINE ATOMS. THE COMPLEX COMPOSITION IS USEFUL IN PREPARING CHROMIUM PLATING BATHS THAT HAVE A BRIGHT PLATING RANGE THAT IS DESIRABLY EXTENDED OVER A BROAD RANGE FOR DECORATIVE CHROMIUM PLATE.

United States Patent O 3,732,270 WERNER CHROMIUM COMPLEXES AND METHODS FOR THEIR PREPARATION John Edwin Bride, Mentor, Ohio, assiguor to E. I. du Pont de Nemours and Company, Wilmington, Del. No Drawing. Filed Feb. 19, 1971, Ser. No. 117,112 Int. Cl. C07f 11/00 US. Cl. 260438.5 C 9 Claims ABSTRACT OF THE DISCLOSURE A Werner complex composition has trivalent chromium atoms coordinated with acido groups and chlorine atoms. The acido groups are from saturated aliphatic dicarboxylic acids having less than six carbon atoms and that may contain hydroxyl groups, but not more than three hydroxyl groups. The complexes are characterized by a specific range for the ratio of both the chromium atoms to acido groups as well as chromium atoms to chlorine atoms. The complex composition is useful in preparing chromium plating baths that have a bright plating range that is desirably extended over a broad range for decorative chromium plate.

BACKGROUND OF THE INVENTION Formerly it has been shown to form complex compounds of the Werner type with trivalent nuclear chromium atoms and acrylic or carbocyclic, carboxylic acido groups, using for the complexing action acids containing ten or more carbon atoms, i.e., typicaly long chain acids. The chromium atoms could also be further coordinated, with neutral or monovalent groups, but this was of secondary importance. Representative of such groups have been the aquo, chloro, fiuoro, bromo, formato, acetato and nitrato groups. The hydrophobic characteristics of surfaces treated with such compositions have been shown, for example, in US. Pats. 2,273,040 and 2,356,161.

It has been further shown, for example in US. Pat. 2,524,803, that there can be produced in a special process, chlorine-containing complexes of the Werner type containing trivalent nuclear chromium atoms coordinated with carboxylic acido groups. In this process although the typically long chain acids such as stearic can be used, and the resulting complex exploited for its hydrophobic quality, shorter chain acids, including aliphatic and aromatic, saturated and unsaturated, and monocarboxylic and dicarboxylic acids, are also employed. These complexes from the shorter chain acids are of interest for their bonding capabilities, especially to polymers, and thus find utility in sizing glass fiber rovings used as plastic and resin reinforcements.

It has also been heretofore taught that acids which are not of the long chain type, and that most especially contain amine groups, but can be simple monocarboxylic acids containing not just one or a few, but very many hydroxyl groups, may be complexed With nuclear trivalent chromium to form compositions of the Werner type. The metal may be further coordinated with neutral groups such as aquo or negative monovalent groups, chloro, bromo, formato, acetato, and nitrato being taught in U .8. Pat. 2,544,668. This patent additionally discloses the desirable bonding between surfaces of diverse materials, particularly polymers, that can be obtained by such Werner complex compounds.

Turning to electrolytic operations, US. Pat. 3,006,823 teaches that oxalic acid may be complexed with trivalent chromium and the complex may be used to form an aqueous electrolytic plating bath for the plating of bright chromium plate. Such bath can be of interest for the capability of depositing an acceptably bright plate at current densities within the range from 10-200 amperes per square foot (a.s.f.).

Further, US. Pat. 2,748,069 shows that plating solutions, of especial interest for use in portable plating devices, may be prepared from complexes of trivalent chromium in association with carboxylic acid and amine constituents. Exemplary acids for the complex include oxalic, succinic, and glutaric. With these amine complexes, plating solutions are worked at a pH of about 7. Further, such solutions are for plating at current densities of about 1,500 to 3,000 a.s.f. and during plating the temperature of the solution may be as high as approximately the boiling point of same. Such has severely detracted from the broad acceptance of these solutions in commercial practice.

SUMMARY OF THE INVENTION The composition of the Werner complex described herein has trivalent chromium atoms coordinated with chlorine atoms and with acido groups of saturated aliphatic dicarboxylic acid having less than six carbon atoms and that may contain hydroxyl groups, but not more than three, and preferably none, or only one hydroxyl group when present at all. The complex finds particular utility in the preparation of an aqueous electrolytic plating bath for the deposition of bright chromium plate. The complex provides a decorative plate with a desirable bright finish and has a desirably extended bright range for the chromium plate. The complex of the present invention exhibits desirable water solubility, plus excellent plating utility over an extended pH range without dissociation or solids precipitation.

Broadly, the invention is directed to a composition of a Werner complex of trivalent chromium atoms coordinated with the acido groups of saturated aliphatic dicarboxylic acid having less than six carbon atoms and 0 to 3 hydroxyl groups, where possible, with the acid providing such complex with a ratio of total chromium atoms to total acido groups within the range of 1:07 to 1:3, such complex being further characterized by containing coordinated chlorine atoms and having a ratio of total chromium atoms to total chlorine atoms within the range of 110.1 to 123.5.

The invention is further directed to the preparation of a composition of a Werner complex containing trivalent chromium atoms coordinated with chlorine atoms and with acido groups of such saturated aliphatic dicarboxylic acid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The complexes of this invention are completely miscible in all proportions in Water and exhibit a rich deep greenish color in water solution. Solubility in organic solvents, for example aprotic organic solvents, will vary according to the particular solvent used, but typically will exhibit greater than slight solubility in dimethylformamide and dimethylacetamide. Solutions exhibit extended storage stability and may be neutralized, or changed over to even an alkaline pH, without solids precipitation.

The complexes of this invention can be prepared by any of several methods. One method is the straightforward combination in aqueous medium of chromium metal, preferably in pulverulent form to enhance completion of the reaction, with the dicarboxylic acid plus chlorine-providing compound. When particulate metal is used, the reaction can be highly exothermic and thus caution needs to be taken in carrying out such reaction. Typically for enhanced reaction efficiency, as the reaction proceeds and the evolved heat starts to diminish, external heating is applied and is continued with the aqueous medium being heated at reflux to augment completion of the reaction.

The complexes may also be prepared by the blending together of the dicarboxylic acid and the chlorine-providing compound in an aqueous reaction medium to which there is charged chromic acid, suitably as a solution of chromic acid in water. The chromic acid can be supplied by any of the substances for forming chromic acid in water, e.g., chromium trioxide. The reaction resulting from this method is also exothermic and caution in the use of such method is also thus advisable.

The saturated aliphatic dicarboxylic acids have less than six carbon atoms and zero to three hydroxyl groups and preferably, for economy and plating efliciency, have two to four carbon atoms with no hydroxyl group. Thus in addition to oxalic acid the acids of particular interest include malonic, with the mono-hydroxy, saturated aliphatic acids such as malic acid being also advantageous. The source of the chlorine atoms for the complex include hydrogen chloride, and gaseous chlorine.

Regardless of the acid used and the source of chlorine, the complex should contain a molar ratio of total chromium atoms to total carboxyl constituent within the range of 1:07 to 1:3, and further contain a molar ratio of total chromium atoms to total chlorine atoms within the range of 120.1 to 123.5. Especially preferred ratios, which are based upon the utility of the complex in an aqueous plating bath for the deposition of decorative chromium plate, can depend upon the acid constituent of the complex. Thus, for example, in a complex where oxalic acid supplies a substantial amount of the carboxyl constituents, the molar ratio of all of the chromium atoms to all of the acido groups, i.e., to carboxyl constituent, is within the range of 1:19 to 1:2.6 and the molar ratio for such a complex of all chromium atoms to the total of the chlorine atoms is preferably within the range of about 1:2.6 to 1:3.2.

For preparing a chromium plating bath for the deposition of bright chromium plate the complex is generally supplied to a plating medium in an amount providing about 25-150 grams of chromium per liter. The more highly concentrated baths are well suited for spot plating techniques while the baths containing the lesser concentrations of chromium are useful for immersing therein articles to be plated. Before deposition of chromium such baths are adjusted to a pH within the range from about 1.8 to 4.9 which can be readily handled by the addiiton of an alkali metal carbonate or hydroxide. The temperature of the bath during plating may range from about 20 C. up to not substantially above about 50 C. for enhanced plating performance.

The bath can also contain a salt of a strong acid preferably, for economy, an alkali metal salt. Such baths may further contain boric acid, or an equivalent to boric acid in aqueous solution, to augment the rate of deposition of the chromium. The alkali metal salts are usually present in an amount of about 50200 grams per liter of the bath and the boric acid in an amount between about 70 grams per liter of the bath. During plating, the object to be plated is made the cathode, for example, immersed in the plating bath, or the cathode in a brush plating operation when the plating medium is contained in a brush, and an inert anode is used, such as a graphite anode. The surfaces that can be plated from such a bath, include metals such as steel, brass, copper, nickel and the like as well as plastic surfaces that are activated or prepared for an electroplating operation. The plating can be carried out in any vessel useful for chromium electroplating such as tanks lined with corrosion resistant materials including glass ceramic material, polyvinyl chloride and the like.

The invention will be further understood by reference to the following illustrative example which should not be construed as limiting the invention.

EXAMPLE Into a container there is placed sufiicient chromium metal, plus oxalic acid, and plus 37.3% strength hydro- 4 chloric acid which is 37.3% by weight HCl in water to provide a molar ratio of chromium to oxalic acid of 1:1.8 and of chromium to chlorine of 1:0.625. The container is covered and good ventilation is provided. After the ingredients are placed together in the container, dissolution of the chromium starts slowly but gradually increases thus supplying heat to the reaction. As the reaction continues and the chromium metal is seen by visual inspection to be substantially dissolved, external heating is applied and the solution is heated at reflux for several hours, and is thereafter permitted to cool.

The resulting chrome complex solution thus prepared there is added sufficient water to form a solution of the complex providing such solution With 40 grams per liter (g./l.) of chromium. The resulting solution is a clear, deep greenish solution that exhibits excellent extended storage stability without solids precipitation or color change. A portion of the chrome complex solution is blended with potassium hydroxide in sufiicient amount to change the pH of the portion from acid, past neutral, over to an alkaline pH greater than 8. Upon visual inspection, such alkaline chrome complex solution is seen to be free from color change or visible solids precipitation.

To demonstrate the plating characteristics of such chromium complex solution, sufiicient complex solution is prepared as described above to contain 40 g./l. of chromium, and to this is blended 60 g./l. of H BO and 150 g./l. of potassium chloride, with agitation. The pH of the solution is adjusted to 3.0 and during blending and pH adjustment the volume of the solution is adjusted to 1 liter by the addition of deionized water.

For this demonstration the resulting solution is placed in a modified Hull cell which is a trapezoidal box of non-conductive material at the opposite ends of which are positioned anode and cathode plates, as has been more particularly described in an article appearing in Plating" Volume 46, Number 3, (1959), Page 257. For this cell it is possible to readily determine the effective plating range of a composition under varying conditions. The current density at any point on a cathode is determined according to the formula A=C(27.748.7 log L) wherein A is the current density in amps per square foot (a.s.f.) at the selected point, C is the total current in amps applied to the cell, and L is the distance in inches of the selected point from the high current density end of the plate. In the cell graphite anodes are used and the cathode is a 3 x 2%" brass panel that is nickel coated prior to use in the cell.

In this cell plating tests are carried out at a bath temperature of F. and at 11.3 volts using 10 amperes current for a 3 minute cycle. From such tests the bright range of decorative chromium plating is seen to be from about 450 a.s.f. down to 9 a.s.f. The panel has a relative reflectance value of about 50% and the deposit has a desirably rich and deep appearance of a slightly darker cast than that observed with commercially available decorative chromium deposits from hexavalent chromium plating baths.

What is claimed is:

1. A composition of a Werner complex of trivalent chromium atoms coordinated With acido groups of saturated aliphatic dicarboxylic acid having less than six carbon atoms and 0 to 3 hydroxyl groups, where possible, said acid providing said complex with a ratio of total chromium atoms to total acido groups within the range of 120.7 to 1:3, said complex being further characterized by containing coordinated chlorine atoms and having a ratio of total chromium atoms to total chlorine atoms within the range of 1:01 to 123.5.

2. A composition as set forth in claim 1 wherein said saturated aliphatic dicarboxylic acid of said Werner complex is selected from the group consisting of oxalic acid, malonic acid, and mixtures thereof.

3. The method for the production of a composition of a Werner complex having trivalent chromium atoms coordinated with chlorine atoms and with acido groups of saturated aliphatic dicarboxylic acid having less than six carbon atoms and to 3 hydroxyl groups, where possible, which method comprises:

(1) establishing a liquid, aqueous reaction medium containing chromium metal, with sufficient of said carboxylic acid to provide said medium with a molar ratio of total chromium atoms to total acido groups within the range of 1:0.7 to 1:3, and with sufficient chlorine-providing compound to supply said reaction medium with a molar ratio of total chromium atoms within the range of 1:01 to 123.5; and

(2) permitting reaction of the substituents in said medium.

4. The process of claim 3 wherein said chlorine compound is selected from the group consisting of hydrogen chlorine, chlorine gas, and mixtures thereof.

5. The process of claim 3 wherein said saturated aliphatic dicarboxylic acid is selected from the group consisting of oxalic acid, ma lonic acid, and mixtures thereof.

6. The process of claim 3 wherein water supplies all of the liquid of said reaction medium, such medium is heated to boiling during reaction, and said chromium metal is in pulverulent form.

7. The process for preparing a composition of a Werner complex containing trivalent chromium atoms coordinated with chlorine atoms and with acido groups of saturated aliphatic dicarboxylic acid having less than six carbon atoms and 0 to 3 hydroxyl groups, where possible, which process comprises:

(1) bringing together in water supplying liquid for a reaction medium, chromic acid with sufiicient of said dicarboxylic acid to provide said medium with a molar ratio of total chromium atoms to total acid groups within the range of 1:0.7 to 1:3, and with chlorine-providing compound sufiicient to supply said medium with a molar ratio of total chromium atoms to References Cited UNITED STATES PATENTS 2,524,803 10/1950 *Iler 260-4385 C 2,273,040 2/1942 Iler 260-4385 C 2,544,666 3/1951 Goebel et al. 260-4385 C 2,544,667 3/1951 Goebel et al. 260-4385 C 2,544,668 3/1951 Goebel ct al. 260-438.5 C 2,825,659 3/1958 Dalton ct a1. 260-4385 C 3,137,717 6/1964 Peters 260-4385 R 3,136,796 6/1964 Trebilcock 260-4385 R 3,185,717 5/1965 Trebilcock 260-4385 R OTHER REFERENCES Sidgwick, The Chemical Elements and Their Compounds, Oxford Univ. Press, London, vol. II, p. 1023 (1950).

Chemical Abstracts, vol. '60, 12247d (1964).

Chemical Abstracts, vol. 44, 3393d (1950).

Chemical Abstracts, vol. 47, 1208715 (1953).

Chemical Abstracts, vol. 41, 2925b (1947).

Chemical Abstracts, vol. 49, 10783g (1955).

HELEN M. S. SNEED, Primary Examiner US. Cl. X.R. 117-1072 Po-ww um'mb STATES PATENT OFFICE 5/ H 69 CERTIFICATE OF CORREC'IION Patent -3-' Dated may 8, 1973 fl I John Edwin Bride I I It is certified that error appears in the above-identified patent and that said LettersPatent are hereby correctad as shown below:'

Column"5, 1ine- 34, "acid" should read acido--.

Signed and sealed this 5th day of March 19m.

(SEAL) Attest:

Commissioner of Patents Atteating' Officer 

